Two lymphokines, migration inhibition factor (MIF) and immune interferon, appear in the serum of mice which have been sensitized to Mycobacterium bovis, strain BCG, and then challenged with specific mycobacterial antigens (old tuberculin). When this lymphokine-containing serum is injected into transplantatble murine tumors it markedly inhibits the growth of those tumors. This model will be used to evaluate the roles of MIF and immune interferon in tumor inhibition. The concentrations of MIF and interferon will be measured to determine if their activities parallel the tumor inhibiting activity of the serum. Purification techniques including salt precipitation, column chromatography and isoelectric focusing will be used to attempt to enrich the factor(s) causing tumor regression and to determine if MIF and interferon activities are separable from the tumor inhibiting activity. Studies will be made to determine physical-chemical characteristics of the tumor inhibitor such as molecular weight, heat stability and sensitivity to enzyme digestion. The mechanism of tumor rejection will be examined. Histologic studies will describe cells present at the tumor site. Inhibitors of lymphocyte and macrophage function will define cell populations required for tumor rejection. In vitro examination of the tumor recipient's antibody and lymphocyte response to tumor cells will show if the host's immune system is involved in the tumor rejection. It is hoped that these studies will help define the role these two lymphokine mediators play in tumor resistance.